Entamoeba histolytica is a widely distributed parasite of humans. The trophozoite or amoebic form can live as a non-virulent commensal in the intestine in asymptomatic carriers or, under stimulus from unknown factors, can breach the intestinal wall and become blood-borne. The circulating parasites often lodge in the liver where they produce liver abscesses that are often fatal. The major long term objective of this research is to understand the basic cell biology and biochemistry of the properties and mechanisms that distinguish virulent and non-virulent amoebae and trigger their interconversion. We propose to continue to use a variety of well established biochemical, morphological and immunological methods to study behavioral and molecular differences between virulent forms of amoebae isolated from liver abscesses and non-virulent forms isolated from asymptomatic carriers. Twenty to thirty independent strains are available in axenic culture for these studies. One general objective of the proposal is to develop immunologic reagents that will allow an unequivocal identification of Entamoeba by species and state of virulence. The detailed specific aims are to: (1) Continue to purify and characterize a membrane associated collagenase from a virulent strain of Entamoeba histolytica. (2) Prepare polyclonal antibodies against the amoeba collagenase and use these to study its function. (3) Prepare hybridomas against Entamoeba surface antigens and use these to study the function(s) of a specific protein and to type strains of Entamoeba. (4) Continue to characterize monoclonal antibodies against Entamoeba actin. (5) Investigate differences in the motility of virulent and non-virulent forms.